In many applications electric motors function as electromechanical actuators with duty cycles requiring rapid braking and then quick reversal of direction. Such duty cycles occur in the operation of rudders, deflectors, spoilers, ailerons, and other flight control surfaces on aircraft. A common manner of decelerating and reversing the direction of rotation of motors, as disclosed by U.S. Pat. No. 3,590,351, is by dynamic braking wherein a resistive load is placed across the motor windings to dissipate the counter-EMF energy generated by the motor as it decelerates. The resulting current produced from the counter-EMF voltage creates a magnetic field in opposition to armature rotation. Major drawbacks of this method of braking an electric motor are that not only is the energy of the counter-EMF wasted, large quantities of heat are generated in addition to the normal heat produced by the motor. Also, if the energy dissipating, resistive load is connected with the power supply system, undesirable high-level electrical transients may be imposed on the other electrical components also coupled to the power supply system.
Another known method of braking electric motors is by changing the energization of the armature windings and/or field of the motor, such as by reversing the direction of the current through the field windings, as disclosed by U.S. Pat. No. 3,541,414. In the '414 patent, the reduction of the field winding current is accomplished by routing the inductive energy of the field winding current back to the field power supply. This technique, however, requires a rather complicated electrical control circuit and also induces undesirable current transients in the power supply. Moreover, the level of the counter-EMF energy recovered by this technique is limited by the voltage level of the power supply.
As noted above, rapid deceleration and reversal of direction of electric motors produces high levels of heat that must be dissipated to prevent damage to the motor components. A common manner of dissipating the heat produced by electric motors is to use the mass of the motor itself and the surrounding structure as a heat sink. However, since many structural components of aircraft are now being constructed from high-strength, nonmetallic materials, such as graphite, boron and kevlar, other methods must be found for controlling the temperatures of motors.
Another common manner of dissipating the heat produced by electric motors is disclosed by U.S. Pat. No. 1,751,424 wherein a primary fan, driven by the output shaft of the motor, and an auxiliary fan, connected to the power supply itself, are employed to circulate air through the motor housing. In addition, in U.S. Pat. No. 3,152,271 Peltier-type thermoelectric devices are used to cool the ferrite permanent magnets that produce the motor field. The thermoelectric devices are powered by the same power supply used to operate the motor. Neither of these two patents involves the use of counter-EMF energy produced by a motor during deceleration to power cooling devices.
Thus, it is a principal object of the present invention to rapidly dynamically brake and reverse the direction of rotation of an electric motor without overheating the motor.
It is a particular object of this invention to divert and then employ the counter-EMF energy recovered from an electrical motor to operate temperature control devices within and remote from the motor.
It is also a particular object of the present invention to pool the counter-EMF energy recovered from a plurality of electric motors and utilize the energy source to cool particular power electronics and/or heat engine fuel as the need arises.